Immersion gold (ENIG)
A chemical displacement reaction deposits a thin gold layer over electroless nickel. Its purpose is protection: the gold stops the nickel oxidising before assembly, and the nickel acts as a diffusion barrier over copper. Thickness is deliberately small.
Hard gold
Electroplated gold with a hardener, typically cobalt or nickel, applied to a defined area such as a card edge or a test point. It is thicker, harder and far more resistant to abrasion. Because it is electroplated, the area needs a plating bus or a conductive connection.
Practical rules
- Soldered pads → immersion gold.
- Repeated insertion / wiping contacts → hard gold.
- Gold wire bonding → a different specification again; discuss the wire and loop before choosing.
- Mixed boards → it is common to have ENIG overall and hard gold only on the connector fingers, applied in a selective step.
State the contact application in the fabrication note. "Gold" alone does not tell the fabricator which process to run.
